t5505: fix pwd on Windows again

The earlier commit b74e70b3 set $PWD to the particular 'pwd' form to use
on Windows and *nix platforms. But this is not good for two reasons: $PWD
has a predefined meaning to the shell (it influences pwd itself), and
all occurrences of 'pwd' must be replaced by $PWD. This new fix now simply
replaces 'pwd' by a shell function on Windows only, where we can be
reasonably certain that 'bash' is in use, so that the function can call
the builtin 'pwd' explicitly.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>

t/t5505-remote.sh

@@ -108,12 +108,11 @@ test_expect_success 'remove remote' '
 '
 
 case $(uname -s) in
-*MINGW*) PWD="pwd -W";;
-*)       PWD=pwd;;
+*MINGW*) pwd() { builtin pwd -W; } ;;
 esac
 cat > test/expect << EOF
 * remote origin
-  URL: $($PWD)/one/.git
+  URL: $(pwd)/one/.git
   Remote branch merged with 'git pull' while on branch master
     master
   New remote branch (next fetch will store in remotes/origin)